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    SubjectRe: [PATCH v2 2/3] kbuild: check the minimum assembler version in Kconfig
    On Tue, Mar 16, 2021 at 1:14 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
    >
    > Documentation/process/changes.rst defines the minimum assembler version
    > (binutils version), but we have never checked it in the build time.
    >
    > Kbuild never invokes 'as' directly because all assembly files in the
    > kernel tree are *.S, hence must be preprocessed. I do not expect
    > raw assembly source files (*.s) would be added to the kernel tree.
    >
    > Therefore, we always use $(CC) as the assembler driver, and commit
    > aa824e0c962b ("kbuild: remove AS variable") removed 'AS'. However,
    > we are still interested in the version of the assembler acting behind.
    >
    > As usual, the --version option prints the version string.
    >
    > $ as --version | head -n 1
    > GNU assembler (GNU Binutils for Ubuntu) 2.35.1
    >
    > But, we do not have $(AS). So, we can add the -Wa prefix so that
    > $(CC) passes --version down to the backing assembler.
    >
    > $ gcc -Wa,--version | head -n 1
    > gcc: fatal error: no input files
    > compilation terminated.
    >
    > OK, we need to input something to satisfy gcc.
    >
    > $ gcc -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
    > GNU assembler (GNU Binutils for Ubuntu) 2.35.1
    >
    > The combination of Clang and GNU assembler works in the same way:
    >
    > $ clang -no-integrated-as -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
    > GNU assembler (GNU Binutils for Ubuntu) 2.35.1
    >
    > Clang with the integrated assembler fails like this:
    >
    > $ clang -integrated-as -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
    > clang: error: unsupported argument '--version' to option 'Wa,'
    >
    > For the last case, checking the error message is fragile. If the
    > proposal for -Wa,--version support [1] is accepted, this may not be
    > even an error in the future.
    >
    > One easy way is to check if -integrated-as is present in the passed
    > arguments. We did not pass -integrated-as to CLANG_FLAGS before, but
    > we can make it explicit.
    >
    > Nathan pointed out -integrated-as is the default for all of the
    > architectures/targets that the kernel cares about, but it goes
    > along with "explicit is better than implicit" policy. [2]
    >
    > With all this in my mind, I implemented scripts/as-version.sh to
    > check the assembler version in Kconfig time.
    >
    > $ scripts/as-version.sh gcc
    > GNU 23501
    > $ scripts/as-version.sh clang -no-integrated-as
    > GNU 23501
    > $ scripts/as-version.sh clang -integrated-as
    > LLVM 0
    >
    > [1]: https://github.com/ClangBuiltLinux/linux/issues/1320
    > [2]: https://lore.kernel.org/linux-kbuild/20210307044253.v3h47ucq6ng25iay@archlinux-ax161/
    >
    > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
    > ---
    >
    > Changes in v2:
    > - Check -integrated-as option instead of error message.
    > - Add LC_ALL=C just in case.
    >
    > The Italian locale did not tweak the message from 'as --version'
    > but we never know what would happen on locale.
    >
    > $ LC_MESSAGES=it_IT.UTF-8 ld --version | head -n 1
    > ld di GNU (GNU Binutils for Debian) 2.35.2
    > $ LC_MESSAGES=it_IT.UTF-8 as --version | head -n 1
    > GNU assembler (GNU Binutils for Debian) 2.35.2
    >
    > Makefile | 4 +-
    > arch/Kconfig | 3 +-
    > init/Kconfig | 12 ++++++
    > scripts/Kconfig.include | 6 +++
    > scripts/as-version.sh | 82 +++++++++++++++++++++++++++++++++++++++++
    > 5 files changed, 104 insertions(+), 3 deletions(-)
    > create mode 100755 scripts/as-version.sh
    >
    > diff --git a/Makefile b/Makefile
    > index cc5b7e39fde4..2b161f5a5a66 100644
    > --- a/Makefile
    > +++ b/Makefile
    > @@ -580,7 +580,9 @@ ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
    > ifneq ($(CROSS_COMPILE),)
    > CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
    > endif
    > -ifneq ($(LLVM_IAS),1)
    > +ifeq ($(LLVM_IAS),1)
    > +CLANG_FLAGS += -integrated-as
    > +else
    > CLANG_FLAGS += -no-integrated-as
    > GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
    > CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
    > diff --git a/arch/Kconfig b/arch/Kconfig
    > index ecfd3520b676..555b4f09a9b2 100644
    > --- a/arch/Kconfig
    > +++ b/arch/Kconfig
    > @@ -631,8 +631,7 @@ config ARCH_SUPPORTS_LTO_CLANG_THIN
    > config HAS_LTO_CLANG
    > def_bool y
    > # Clang >= 11: https://github.com/ClangBuiltLinux/linux/issues/510
    > - depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD
    > - depends on $(success,test $(LLVM_IAS) -eq 1)
    > + depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD && AS_IS_LLVM
    > depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
    > depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
    > depends on ARCH_SUPPORTS_LTO_CLANG
    > diff --git a/init/Kconfig b/init/Kconfig
    > index 5f5c776ef192..019c1874e609 100644
    > --- a/init/Kconfig
    > +++ b/init/Kconfig
    > @@ -41,6 +41,18 @@ config CLANG_VERSION
    > default $(cc-version) if CC_IS_CLANG
    > default 0
    >
    > +config AS_IS_GNU
    > + def_bool $(success,test "$(as-name)" = GNU)
    > +
    > +config AS_IS_LLVM
    > + def_bool $(success,test "$(as-name)" = LLVM)
    > +
    > +config AS_VERSION
    > + int
    > + # Use clang version if this is the integrated assembler
    > + default CLANG_VERSION if AS_IS_LLVM
    > + default $(as-version)
    > +
    > config LD_IS_BFD
    > def_bool $(success,test "$(ld-name)" = BFD)
    >
    > diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
    > index 58fdb5308725..0496efd6e117 100644
    > --- a/scripts/Kconfig.include
    > +++ b/scripts/Kconfig.include
    > @@ -45,6 +45,12 @@ $(error-if,$(success,test -z "$(cc-info)"),Sorry$(comma) this compiler is not su
    > cc-name := $(shell,set -- $(cc-info) && echo $1)
    > cc-version := $(shell,set -- $(cc-info) && echo $2)
    >
    > +# Get the assembler name, version, and error out if it is not supported.
    > +as-info := $(shell,$(srctree)/scripts/as-version.sh $(CC) $(CLANG_FLAGS))
    > +$(error-if,$(success,test -z "$(as-info)"),Sorry$(comma) this assembler is not supported.)
    > +as-name := $(shell,set -- $(as-info) && echo $1)
    > +as-version := $(shell,set -- $(as-info) && echo $2)
    > +
    > # Get the linker name, version, and error out if it is not supported.
    > ld-info := $(shell,$(srctree)/scripts/ld-version.sh $(LD))
    > $(error-if,$(success,test -z "$(ld-info)"),Sorry$(comma) this linker is not supported.)
    > diff --git a/scripts/as-version.sh b/scripts/as-version.sh
    > new file mode 100755
    > index 000000000000..953ff000bcbc
    > --- /dev/null
    > +++ b/scripts/as-version.sh
    > @@ -0,0 +1,82 @@
    > +#!/bin/sh
    > +# SPDX-License-Identifier: GPL-2.0-only
    > +#
    > +# Print the assembler name and its version in a 5 or 6-digit form.
    > +# Also, perform the minimum version check.
    > +# (If it is the integrated assembler, return 0 as the version, and
    > +# skip the version check.)
    > +
    > +set -e
    > +
    > +# Convert the version string x.y.z to a canonical 5 or 6-digit form.
    > +get_canonical_version()
    > +{
    > + IFS=.
    > + set -- $1
    > +
    > + # If the 2nd or 3rd field is missing, fill it with a zero.
    > + #
    > + # The 4th field, if present, is ignored.
    > + # This occurs in development snapshots as in 2.35.1.20201116
    > + echo $((10000 * $1 + 100 * ${2:-0} + ${3:-0}))
    > +}
    > +
    > +# Clang failes to handle -Wa,--version fails unless -no-integrated-as is given.

    This line got strange after some editing.

    I will rephrase it to:

    Clang fails to handle -Wa,--version unless -no-integrated-as is given.





    > +# We check -(f)integrated-as, expecting it is explicitly passed in for the
    > +# integrated assembler case.
    > +check_integrated_as()
    > +{
    > + while [ $# -gt 0 ]; do
    > + if [ "$1" = -integrated-as -o "$1" = -fintegrated-as ]; then
    > + # For the intergrated assembler, we do not check the
    > + # version here. It is the same as the clang version, and
    > + # it has been already checked by scripts/cc-version.sh.
    > + echo LLVM 0
    > + exit 0
    > + fi
    > + shift
    > + done
    > +}
    > +
    > +check_integrated_as "$@"
    > +
    > +orig_args="$@"
    > +
    > +# Get the first line of the --version output.
    > +IFS='
    > +'
    > +set -- $(LC_ALL=C "$@" -Wa,--version -c -x assembler /dev/null -o /dev/null 2>&1)
    > +
    > +# Split the line on spaces.
    > +IFS=' '
    > +set -- $1
    > +
    > +min_tool_version=$(dirname $0)/min-tool-version.sh
    > +
    > +if [ "$1" = GNU -a "$2" = assembler ]; then
    > + shift $(($# - 1))
    > + version=$1
    > + min_version=$($min_tool_version binutils)
    > + name=GNU
    > +else
    > + echo "$orig_args: unknown assembler invoked" >&2
    > + exit 1
    > +fi
    > +
    > +# Some distributions append a package release number, as in 2.34-4.fc32
    > +# Trim the hyphen and any characters that follow.
    > +version=${version%-*}
    > +
    > +cversion=$(get_canonical_version $version)
    > +min_cversion=$(get_canonical_version $min_version)
    > +
    > +if [ "$cversion" -lt "$min_cversion" ]; then
    > + echo >&2 "***"
    > + echo >&2 "*** Assembler is too old."
    > + echo >&2 "*** Your $name assembler version: $version"
    > + echo >&2 "*** Minimum $name assembler version: $min_version"
    > + echo >&2 "***"
    > + exit 1
    > +fi
    > +
    > +echo $name $cversion
    > --
    > 2.27.0
    >
    > --
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    --
    Best Regards
    Masahiro Yamada

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